1. Field of the Invention
This invention relates to a lens barrel having driving device for driving a lens.
2. Related Background Art
In many photographing systems, a driving device capable of effecting highly accurate movement free of back-lash has heretofore been demanded for an apparatus for performing the operation of rotating or rectilinearly moving a lens holding cylinder when the zooming operation or the focusing operation is performed.
For example, U.S. Pat. No. 4,386,829 proposes a moving device for a lens holding cylinder which uses appropriately constructed cam means to make highly accurate movement possible.
In this patent, a cam portion is provided in a portion of the lens holding cylinder movable by the rotating operation such as the zooming operation or the focusing operation. This cam portion is provided with two cam surfaces, and a rectilinear movement groove intersecting these cam surfaces is formed in a fixed cylinder, a key member is fitted into this rectilinear movement groove, a pillar-like cam follower which is in contact with one of the cam surfaces of the cam portion is secured to the key member, a groove is formed in the key member, and a pillar-like projected piece which is in contact with the other cam surface of the cam portion is engaged with the groove. The cam follower and the projected piece are tensioned by a spring extended in the groove of the key member, and the cam follower and the projected piece are biased against the cam surfaces of the cam portion, thereby providing a moving device for a lens holding cylinder in which the creation of back-lash is prevented.
In the moving device for the lens holding cylinder proposed in the aforementioned U.S. Pat. No. 4,386,829, when for example a strong shock force is applied to the lens holding cylinder, the cam surfaces of the cam portion may be flawed or scarred by the cam follower. If the cam surfaces are flawed or scarred, back-lash will be created in the lens holding cylinder, for example, by zooming, to thereby deteriorate the optical performance remarkably.
Against this, the assignee hereof has proposed in U.S. Pat. No. 4,465,344 a moving device for a lens holding cylinder in which the radius of the portion of a cam follower which is in contact with a cam surface is made great to thereby prevent the cam surface or the protective wall surface from being flawed when a shock force is applied to the lens holding cylinder.
Members constituting a lens barrel structure, for example, a lens fixing cylinder and a cam cylinder having a cam for regulating a lens unit for movement, have heretofore been molded and manufactured by the use of a plastic material. There have been proposed various lens driving devices in which the cam cylinder provided by such a method is rotated or rectilinearly moved to change the position thereof on the optic axis, thereby accomplishing focusing or magnification change.
U.S. Pat. No. 4,707,083 proposes a lens moving device in which a guide pin bears against the side of one of cam slots formed in a fixed cylinder and a cam cylinder and having a predetermined angle of inclination and the guide pin is biased by spring means and the guide pin engaged at the point of intersection between the two cam slots is utilized to move a movable lens frame in the direction of the optic axis and accomplish magnification change.
In the lens moving device according to the prior art, cam slots are formed in both of the fixed cylinder and the cam cylinder and a cam follower engaged at the point of intersection between the two cam slots is utilized to move the lens frame.
Therefore, the space of the cam slots becomes wide in a lens barrel for a lens frame which is great in the amount of movement, and this has led to the problem that the cam cylinder becomes weak in terms of strength and the outer peripheral surface of the lens barrel cannot be used intact as an exterior part.
As a countermeasure for these problems, there has also been proposed a cam cylinder in which a wall is left on the outer peripheral surface of a cam slot, but this method has suffered from the problem of adopting such complicated mold structure that a mold must be slidably moved toward the inner peripheral surface side or must be parted while being rotated when the cam cylinder is molded by the use of a plastic material.
Also, in the lens moving device of the aforementioned U.S. Pat. No. 4,386,829, a convex cam is formed in a curved shape and therefore, one of cam followers becomes displaceable by a spring, and this has led to the tendency that assembly and adjustment become difficult.